چكيده به لاتين
Although cement has excellent properties and high performance, but inherent brittleness is a major drawback. Recently, adding nanoparticles to cement-based materials due to their high surface area and the ability to change the cement microstructure has attracted much attention. In this research, the effect of adding different sizes of magnetite nanoparticles on the mechanical and physical properties of the ordinary Portland cement (OPC) was initially studied.Cement paste with a water to cement ratio of 0.5 was prepared. To study the effect of the size of the magnetite particles, different cement samples containing 0.2 wt.% Fe3O4 additives with four different particle sizes (20-40 nm, 80-100 nm, 250-300 nm and 2-1 μm) were fabricated. Cement paste mixed with magnetite for compressive strength, flexural strength, indirect tensile strength, XRD analysis and SEM images were evaluated. The results of mechanical strength showed that hardened cement paste containing magnetite nanoparticles with the size of 20-40 nm exhibited higher compressive strength, flexural strength and tensile strength compared to the other samples for all ages of hydration. This sample also had the best results in porosity, ultrasonic pulse velocity, water sorptivity and electrical resistivity. Therefore, magnetite nanoparticles of 20-40 nm were selected as the optimum additive. In order to investigate the effect of the amount of this type of nanoparticles, magnetite nanoparticles were added at different amounts of 0.1, 0.15, 0.2, 0.25, 0.3, and 0.35% by weight of cement. It was found that the sample containing 0.25 wt.% Fe3O4 nanoparticles revealed the best results in all properties. The addition of 0.25 wt.% of magnetite nanoparticles of 20-40 nm to cement paste at the age of 7 days increased compressive strength, flexural strength and tensile strength by 32, 25 and 19%, respectively. In addition, porosity and secondary water absorption decreased by 19% and 11%, respectively, at the age of 7 days. In the third satge of the project, hybrid nanocomposite of Fe3O4-GO was used to reinforce the cement paste. Adding graphene-magnetite oxide nanocomposite to cement paste improved the mechanical and physical properties of the neat cement and Fe3O4-reinforced cement due to increasing surface roughness og GO and better dispersion of additive nanoparticles. The optimum amount of Fe3O4-GO (0.05 wt.% GO, 0.25 wt.% Fe3O4) nanocomposite at the age of 7 days increased the compressive, flexural and tensile strengths by 53, 93 and 85 %, respectively. Furthermore, porosity and secondary sorptivity decreased by 31% and 44% at the age of 7 days. Microsturctural studies showed that graphene oxide-magnetite nanocomposite, by creating a very dense and interconnected structure, caused distortion of cracks and improved crack annihilation.
